virtio_console: silence a static checker warning

My static checker complains that this sprintf() can overflow but really
it can't.  Just silence the warning by using snprintf().
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/char/virtio_console.c

@@ -1492,7 +1492,7 @@ static int add_port(struct ports_device *portdev, u32 id)
 		 * Finally, create the debugfs file that we can use to
 		 * inspect a port's state at any time
 		 */
-		sprintf(debugfs_name, "vport%up%u",
+		snprintf(debugfs_name, sizeof(debugfs_name), "vport%up%u",
 			 port->portdev->vdev->index, id);
 		port->debugfs_file = debugfs_create_file(debugfs_name, 0444,
 							 pdrvdata.debugfs_dir,